[Dovecot] Dovecot aspects of fighting spam

[Rainer Frey]

On Tuesday 01 June 2010 15:42:18 Phil Howard wrote:
> I see no documents in the Dovecot documents wiki on how Dovecot
> features can be used in the fight against spam.  One hit came up in a
> search, and it was about how to fight spam in the MoinMoin Wiki itself
> (e.g. TextCHAs and such).

I guess you'll have the mental transfer of "fight spam" into "cause dovecot to 
perform this and that action" yourself. The possible actions are, in general, 
documented.

> I already asked in another thread about removing message files at the
> search from a designated "learn-spam" folder.  My next question would
> be how to automatically place detected spam into a specific folder for
> the user to access or ignore as they deem fit.  

You need to configure the MTA to accept and tag spam messages, e.g. with 
Amavis D_PASS policy and appropriate tag levels. Then the most flexible way to 
put the mails into a spam folder is to use the deliver plugin for sieve, which 
can sort and filter mails depending on many different conditions, like 
presence and/or value of any header. You can deploy a single system wide 
default script for all users, which can be complemented or overwritten by 
individual users (depending on configuration).

See http://wiki.dovecot.org/LDA/Sieve
If you use dovecot 1.2, using the new Dovecot Sieve plugin is highly 
recommended above the  old CMUsieve.
See http://wiki.dovecot.org/LDA/Sieve/Dovecot

The really recommended way nowadays is different though: *reject* as much spam 
as possible in the MTA in the receiving SMTP dialog, with a combination of 
blacklists, sender validation (e.g.DKIM), potentially greylisting (as you deem 
appropriate) and lastly content scanning with s.th. like amavis+spamassassin. 
I'd not expect a noticable amount of false positives, and in the rare cases 
the sender will be notified. The false positives rate of users scanning 
through a folder of tagged mail will be higher.

> A wiki document on how Dovecot helps (or how to help Dovecot) in the
> fight against spam, I think, would be helpful.

A howto-like page to describe the usage of some dovecot features in an anti-
spam context wouldn't hurt, OTOH there is not much anti-spam specific stuff at 
all at the dovecot side.

Rainer